The caller claimed knowledge of Josef Mengele, the former Nazi chief physician at the Auschwitz death camp. After a brief conversation, Wiesenthal made an appointment to interview the caller.

"I've never had so much information on Mengele," the world's best-known Nazi-chaser said.

For the portly, 76-year-old Austrian Jew, who has spent the better part of four decades pursuing Nazi war criminals, 1985 shapes up as one of his most hectic yet potentially promising years.

Widely publicized 40th anniversary commemorations related to the end of World War II have jogged long-hidden memories, generating a miniature boom of information for him and his Vienna-based Documentation Center of the Federation of Jewish Victims of Nazism.

In the past, a lack of such interest has contributed to delays in apprehending suspected Nazi war criminals and, because of those delays, there have been some bitter disappointments for Wiesenthal and others.

By the time the former Gestapo chief from northern Yugoslavia, Clemens Druschke, was brought to trial last year-- for example, the fading memories of key witnesses and the deaths of others weakened testimony to a point that a Duesseldorf jury had little option but to acquit him.

Efforts to extradite Walter Rauff, who organized convoys of mobile gas chambers that brought death to an estimated quarter of a million people, failed when Rauff died in Chile late last year. His death came only days before a West German courier, dispatched with a fully documented charge sheet, was scheduled to depart for Santiago, where Rauff had lived since the early 1960s.

But neither setbacks nor advancing years appear to have sapped the energy of the grandfatherly Wiesenthal, who is obviously buoyed by the renewed activity.

"I don't have time to slow down," he said in a recent interview. "There is too much to do."

His fourth-floor office looks it.

Books, documents and reams of loose paper fill bookcases, spill from his overloaded desk onto surrounding tables and strain the springs of a dilapidated couch nearby. Each day's mail, invariably containing new tips, merely adds to the paper volume.

Relatively Little Authentic

Indeed, much of Wiesenthal's work day is spent trying to sift the few genuine leads from the flow of largely bogus information, a talent that he says has become more instinctive than objective over the years.

"Sometimes I can pick up a letter and, by its feel, know that something worthwhile is inside," he said.

But even when skeptical, Wiesenthal tends to listen.

After hearing a caller from Switzerland describe a letter that was supposedly signed by Mengele, Wiesenthal countered, "I get letters from Martin Bormann out of Cairo addressed to me, but I don't think they are real." (In 1973, after identification of a skeleton, West Germany formally declared that Bormann, Hitler's closest personal aide, committed suicide in 1945--a conclusion reached by some historians in the early 1950s).

Still, Wiesenthal agreed to discuss the matter further with the tipster.

Possible Emigres

Amid this paper jungle, the Nazi-hunter talked of his current work. There is the search for 1,800 non-Germans, mainly East Europeans, who once belonged to Hitler's SS units and who may have emigrated to the United States or to other Western countries.

There are also more than 200 Ukrainian SS officers, some of whom may have emigrated to Canada. And, of course, there is Mengele.

January's anniversary of the liberation of Auschwitz, current U.S. congressional hearings and a formal Justice Department investigation have all focused interest on Mengele--the most widely known Nazi war criminal still believed alive and at large.

Although Wiesenthal describes the search for the former Auschwitz doctor as only one of many cases, he concedes that it is currently the most important.

Nicknamed the "Angel of Death," Mengele supervised prisoner arrivals at Auschwitz, deciding with a wave of his white-gloved hand which Jews went directly to the gas chambers and which would survive for forced labor.

Experiments With Twins

His fascination with twins led to macabre, excruciatingly painful experiments that often resulted in death or mutilation of the victims.

Wiesenthal holds Mengele responsible for the death of 300,000 to 400,000 Jews at Auschwitz.

Mengele slipped out of Allied hands after the war and eventually surfaced in South America, where reports periodically place him and where many believe he still lives.

If he is alive, Mengele would be 74 on March 16.

Periodically, accounts of his death have circulated, but Wiesenthal is convinced that these are false and that Mengele most likely lives on a military reservation in Paraguay, about 200 miles south of the capital, Asuncion.